Circular hosiery knitting machines are known which have two coaxial and mutually facing beds and are constituted for example by a needle cylinder, which has a vertical axis, and by a dial, which is arranged above and coaxially with respect to the needle cylinder.
A plurality of axial slots are provided on the lateral surface of the needle cylinder, and each slot accommodates a needle which can be actuated with a reciprocating motion along the corresponding axial slot in order to produce knitting.
In the dial of these machines a plurality of radial slots are provided, each of which accommodates at least one engagement element, which can be constituted by a hook or by a pusher or by a needle, which can move on command along the corresponding radial slot in order to pass from an extracted position, in which it protrudes from the peripheral profile of the dial, to a retracted position, in which it is recessed within the dial in order to avoid interfering with the needles of the needle cylinder.
In the extracted position, the engagement elements can interact with at least one needle of the needle cylinder in order to engage a loop of knitting or more generally a portion of a row of knitting produced by the needles of the needle cylinder or in order to release a loop of knitting or a portion of a row of knitting engaged previously to a needle of the needle cylinder.
In the retracted position, the engagement elements can retain the loop of knitting or portion of row engaged previously without interfering with the needles of the needle cylinder.
Depending on the type of engagement elements used, the engagement elements can pick up loops of knitting, in the strict sense of the term, from the needles that have produced them or can retain portions of loop linking yarn during the formation of a row of knitting by the needles of the needle cylinder and then release to the needles of the needle cylinder the loops of knitting previously picked up or the portions of loop linking yarn previously retained. For the sake of simplicity in presentation, the expression “loop of knitting” is understood hereinafter to designate a portion of a row of knitting which can be constituted by a loop of knitting in the strict sense of the term or by a portion of loop linking yarn.
In some machines, each engagement element is constituted by two or more elements arranged side-by-side, which are generally arranged in a same radial slot of the dial and cooperate with each other and with the needles of the needle cylinder in order to pick up loops of knitting from the needles of the needle cylinder or release to the needles of the needle cylinder loops of knitting previously picked up by other needles of the needle cylinder or retained during the formation of a row of knitting on the part of the needles of the needle cylinder.
If the engagement elements arranged in the dial are constituted by needles, said needles, in addition to being usable to engage or pick up loops of knitting produced by the needles of the needle cylinder, can also be used to produce knitting.
In the field of the production of items of clothing known as “seamless”, i.e., items of clothing which have a tubular structure without seams at their lateral regions, the need is felt to be able to join portions of knitting, produced by groups of needles which are arranged in the needle cylinder and are mutually angularly spaced around the axis of the needle cylinder, so as to avoid the need to subsequently rework the item of clothing in order to produce the seam for joining said portions of knitting.
A need of this kind occurs for example for the shoulder straps of vests, bras, body suits or for the crotch of underpants.